Conventionally the so-called “HIMU” (High U/Pb Mantle) ocean islands have been considered as representing subducted basaltic ocean crust that has cycled through the mantle to become part of mantle plumes. This paper by Weiss et al. presents a radically different interpretation, that the HIMU ocean island mantle source represents subcontinental lithospheric mantle (SCLM) that was metasomatized by carbonatitic fluids. In order to become a plume, the metasomatized SCLM had to delaminate from the lithosphere into the convecting mantle, and be transported to a mantle boundary layer, probably the core–mantle boundary, where it later became part of upwelling mantle plumes.

Reflecting on the use of PetDB data for this study, the authors state: “We are writing to you about it because the xenolith data in PetDB was critical for us to be able to publish it. A reviewer brought up some important issues that questioned whether the SCLM can be the HIMU mantle source. We were able to address these issues because PetDB allowed us to easily access essentially the entire body of published xenolith data, which would have been impractical for us to compile by ourselves. This was a key factor for the publication of this study because it gave us a broad overview of the composition of the SCLM, including the information we needed to confirm that our conclusions are viable.”

Figure 4. Conceptual model for the evolution of the HIMU mantle source.